1. Field of the Invention
The present invention relates to an organic light emitting device. More specifically, the present invention relates to a white organic light emitting device in which efficiency is improved by specifying an energy level of a hole transport layer or a blocking layer adjacent to a light emitting layer.
2. Discussion of the Related Art
The recent trend toward information-dependent age has brought about rapid development in display fields that visually display electrical information signals. In this regard, a variety of flat display devices having superior properties such as slimness, low weight and low power consumption are developed and are actively used as substitutes of conventional cathode ray tubes (CRTs).
Specific examples of flat display devices include liquid crystal display devices (LCDs), plasma display panel devices (PDPs), field emission display devices (FEDs), organic light emitting devices (OLEDs) and the like.
Among them, organic light emitting devices that do not require an additional light source, realize a compact design and render clear color are considered to be competitive applications.
Such organic light emitting devices require formation of organic light emitting layers.
An organic light emitting device rendering white light that is designed by laminating a stack structure including organic light emitting layers having different colors without patterning the organic light emitting layers at respective pixels was suggested.
That is, in white organic light emitting devices, light emitting diodes are formed by depositing layers between an anode and a cathode without using a mask, and organic films including organic light emitting layers are sequentially deposited under vacuum using different materials.
White organic light emitting devices are utilized in various applications including thin light sources, backlights of liquid crystal display, or full-color displays using color filters.
Meanwhile, each stack of conventional white organic light emitting devices includes a hole transport layer, a light emitting layer, and an electron transport layer.
In this regard, in a conventional white organic light emitting device having a configuration in which an electron transport layer is adjacent to the light emitting layer, electrons or excitons generated in the light emitting layer are not used for light emission and are introduced into the hole transport layer. For this reason, luminous efficiency of the light emitting layer is disadvantageously deteriorated.
These conventional white organic light emitting devices have the following problems.
When the triplet energy level of the light emitting layer is similar to that of the hole transport layer, electrons or excitons generated in the light emitting layer are not used for light emission and are introduced into the hole transport layer. For this reason, luminous efficiency of the light emitting layer is disadvantageously deteriorated.